1. Field of the Invention
This invention relates to baffling of stray light in a conformal (non-spherical) dome to prevent its entry into the aperture of the receiver optics and sensor, and, more particularly, the baffling of stray light in a conformal optic two-axis seeker provided with arch corrector optics mounted on the outer gimbal.
2. Description of the Related Art
An optical system includes an optical train with a sensor that receives radiated energy from a scene and converts it to an electrical signal. The electrical signal is processed to compute a guidance command, provided to a display or further processed for automated pattern recognition. The sensor is fragile and is easily damaged by dirt, erosion, chemicals, or high air velocity. In some systems the optical trains are fixed in orientation, and others the optical trains are mounted on gimbals that rotate to allow sensing over a wide angular field of regard.
In service, the sensor is placed behind a transparent, flat or dome-shaped window through which it views the scene and which protects the sensor from such external effects. If the dome-shaped window is non-spherical, highly curved, or thick, the window may introduce significant wavefront aberration into the optical rays that pass through it on the way to the sensor. These domes are typically referred to as a “conformal” dome, window or optic. Conformal domes present significant advantage in aerodynamic performance while presenting greater optical challenges. As discussed in U.S. Pat. No. 6,028,712, a transparent optical corrector having a shape responsive to the shape of the dome may be placed on the outer gimbal in the optical path between the conformal dome and the sensor to compensate for the aberrations introduced by the non-spherical window.
Reflections from one or more surfaces of transparent material may introduce stray light rays into the optical system that are unrelated to the scene light rays that are the subject of interest. In the optical system, the stray light rays, if reflected into the aperture of the receiver optics and to the sensor, may be misinterpreted as having come from the scene, may obscure the scene, or may blind the sensor if sufficiently strong. One particularly troublesome source of stray light rays is the sun. Even after the light rays of the sun are reflected multiple times, they may still be orders of magnitude brighter than objects of interest in the scene.
U.S. Pat. No. 6,462,889 discloses rotationally symmetric stationary optical baffles to reduce stray light rays that are reflected into a fixed optical train. At least one light baffle is positioned in the optical path between the outer dome and the sensor system and is fixed in space relative to the central axis. There are typically from one to three baffles, each affixed to either the inter surface of the outer dome or to the optical corrector. Each baffle is a frustoconical tube that is rotationally symmetric about the central axis. A set of fins may be supported on one of the baffles, with each fin extending radially outwardly from an outer surface of the baffle and parallel to the central axis.
U.S. Pat. No. 6,028,712, which is hereby incorporated by reference, discloses an optical corrector for gimbal-mounted optical trains. The optical system includes a housing having an axis of elongation (e.g. the central axis), and a non-spherical window affixed to the housing. An optical corrector, preferably in the form of an aspherical strip of transparent material, is positioned adjacent to the curved inner surface of the window. The optical corrector is mounted on an optical corrector support, which is rotatable about the axis of elongation (e.g. the roll axis which is coincident with the central axis). An optical train is positioned such the optical corrector lies between the window and the optical train. The optical train includes at least one optical element operable to alter an optical ray incident thereon, and a gimbal upon which at least one optical element is mounted. The gimbal is pivotable about a transverse axis (e.g. the nod axis) perpendicular to the axis of elongation (the roll axis). The optical train is mounted on an optical train support, which is movable independently of the optical corrector support. A sensor is positioned to receive the optical ray passing sequentially through the window, the optical corrector, and the optical train. The described optical corrector is hereafter referred to as an “arch corrector”. The arch corrector is suitably used with a conformal dome roll/nod seeker.
U.S. Pat. No. 6,310,730, which is hereby incorporated by reference, discloses an optical corrector for gimbal-mounted optical trains. The optical system includes a curved window, an asymmetric, scoop-shaped optical corrector adjacent to a curved inner surface of the window, an optical train positioned such that the optical corrector lies between the curved window and the optical train, a movable optical train support upon which the optical train is mounted, and a sensor disposed to receive an optical ray passing sequentially through the window, the optical corrector, and the optical train. The optical corrector has an inner surface and an outer surface, at least one of which has a shape defined by an asymmetric polynomial. The described optical corrector is hereafter referred to as a “half-arch corrector”. The scoop-shaped optical corrector may be mounted on a roll gimbal to rotate about the roll axis. At least the forward most receiver optic of the optical train rotates about a nod axis such that the optical corrector remains in the optical path between the window and the forward most optic. The “half-arch” corrector is lighter weight than the “arch” corrector but requires the optical train to roll more to cover the same field of regard (FOR).